The present invention relates to a control system for an internal combustion engine equipped with a compression ratio control mechanism capable of varying a compression ratio, a lift and operation angle control mechanism capable of varying a lift and operation angle of an intake valve, and a phase control mechanism capable of varying a maximum lift phase of an intake valve. The present invention further relates to a method for controlling such an internal combustion engine. Still further, the present invention relates to a technique for improving the exhaust gas purifying efficiency of a spark-ignited internal combustion engine equipped with a catalytic exhaust gas purifier.
The assignee of this application has heretofore proposed a variable valve timing control mechanism that can vary the lift and operation angle of an intake valve simultaneously and continuously as disclosed in Japanese Patent Provisional Publication Nos. 11-107725 and 11-324625. The assignee has further proposed a variable valve timing control mechanism that can attain a wide design freedom of the lift characteristics in combination with a phase control mechanism for varying a maximum lift phase.
Further, it has been proposed, as disclosed in Japanese Patent Provisional Publication No. 2000-73804, a double-like type piston-crank mechanism that serves as a variable compression ratio control mechanism for a reciprocating internal combustion engine.
As is well known, an exhaust system of an internal combustion engine is provided with a catalytic exhaust gas purifier made up of an oxidation-reduction catalyst, oxidation catalyst or a reduction catalyst. However, even by the advanced catalyst technology of today, it is the present situation that the catalyst effect on the gas emitted from the engine is largely limited immediately after cold start at which the catalyst temperature is low as compared with that after warming up of the engine. This problem has long been recognized by the person skilled in the art. Thus, a continuous effort has been made to lower the active temperature of the catalyst and it has been devised to introduce the secondary air into the upstream side of the catalyst for thereby advancing the time at which the catalyst is chemically activated.
However, the fundamentals to solving such a problem are how fast the catalyst can reach the temperature at which the catalyst starts conversion. To this end, the ignition timing is delayed during warming up (i.e., the exhaust gas temperature is elevated by retarding the timing at which combustion starts). This, however, causes a bad influence on the fuel consumption but is widely exercised. However, if the ignition timing is retarded largely, there is caused a problem that the combustion becomes unstable and in the worst case a misfire is caused and therefore a large amount of unburnt substances as HC is possibly emitted. Accordingly, for largely retarding the ignition timing, it is indispensable to improve the combustion. Heretofore, it is a representative method for improving the combustion under those circumstances to provide the intake port with a swirl control valve for intensifying the gas flow within the cylinder, but this is not always sufficient.
It is accordingly an object of the present invention to provide a control system for an internal combustion engine having a compression ratio control mechanism, a lift and operation angle control mechanism and a phase control mechanism, which can provide an improved combustion control at cold engine operation and thereby attain a considerably improved exhaust gas purifying efficiency.
It is a further object of the present invention to provide a method for controlling an internal combustion engine, which is carried out by the control system of the foregoing character.
According to an aspect of the present invention, there is provided a control system for an internal combustion engine having a compression ratio control mechanism capable of varying a compression ratio of the engine, an ignition timing control system capable of varying an ignition timing of the engine, and a catalytic exhaust gas purifier disposed in an exhaust system of the engine, the control system comprising an engine control unit for controlling the compression ratio control mechanism and the ignition timing control system so that the compression ratio is varied depending upon variations of engine rpm, engine load and a warm-up condition of the engine and that when the engine is cold, the ignition timing is retarded largely from an MBT point and the compression ratio is set higher than that obtained when the engine is hot and operated at corresponding engine rpm and engine load.
According to another aspect of the present invention, there is provided an internal combustion engine comprising a compression ratio control mechanism capable of varying a compression ratio of the engine, an ignition timing control system capable of varying an ignition timing of the engine, a catalytic exhaust gas purifier disposed in an exhaust system of the engine and an engine control unit for controlling the compression ratio control mechanism and the ignition timing control system so that the compression ratio is varied depending upon variations of engine rpm, engine load and a warm-up condition of the engine and that when the engine is cold, the ignition timing is retarded largely from an MBT point and the compression ratio is set higher than that obtained when the engine is hot and operated at corresponding engine rpm and engine load.
According to a further aspect of the present invention, there is provided a method for controlling an internal combustion engine having a compression ratio control mechanism capable of varying a compression ratio of the engine, an ignition timing control system capable of varying an ignition timing of the engine, and a catalytic exhaust gas purifier disposed in an exhaust system of the engine, the method comprising controlling the compression ratio control mechanism and the ignition timing control system so that the compression ratio is varied depending upon variations of engine rpm, engine load and a warm-up condition of the engine and that when the engine is cold, the ignition timing is retarded largely from an MBT point and the compression ratio is set higher than that obtained when the engine is hot and operated at corresponding engine rpm and engine load.